What's the model number pls?
Upgrade the latest firmware, reset and reconfigure it to see if the problem continues.

Sorry, Archer C2 AC750

I did a firmware upgrade, but looked like the same version but didn't hurt to do it anyway.

No change after the upgrade and reboot, disabled guest network was still showing. Then did a restore to factory settings and setup again, this time without setting up and disabling Guest. Guest does not show (as expected really).

Next enabled and then disabled Guest network. It has now gone. Looks like a combination of reloading the Firmware and restore to factory settings has cleared the issues.

Thanks for posting! I bought two Archer C2 V1 routers a while back to upgrade my older junk and just last weekend got around to installing them. I have upgraded both to the newest firmware level. I can turn off the guest networks, but the SSIDs still seem to be broadcasted. One is configured as the main router and in the other end of the house the second is configured as just a wifi access point.I will try the reset to factory defaults and turn off guest networking FIRST, before I update any other settings. (I do not need a guest network, the few friends we have visit are advised of the key when they need it.) I did fiddle with settings quite a bit, I must have confused the poor little things.

The most important feature on these routers? The ON/OFF button!!!

Anyone need a bunch of old assorted make/model routers? I have a pile of four on my desk now... Yeah, i upgrade fairly often. I buy a few notches behind the latest and greatest to be able to feed my upgrade habit.

NCC1701 wrote

the second is configured as just a wifi access point.

Keep in mind that if you have guest mode enabled when set up as a wifi access point, it'll let guests connect to everything on your network behind the access point :(

-Jamie M.